Alright guys I have a Pontiac G6 '06. Electrical consists of Tenny's Alt 250 amp alt, Red Top Optima up front, C&D 100AH in trunk, Big 3. Now I idle very low! 11.8-12v, however at about 1500-2000rpms I'm back up to 14.5-14.8 instantly. I've tried just about everything. I've gotten a tune up, just installed brand new battery cables. Iirc the low idle still existed before the alt change. Red Top is maybe 2-3 years old, I bought it brand new. Alt is still very new 6 months or so.